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On The NCAA Bubble? Here’s The Number To Watch

College basketball season is in its final sprint toward Selection Sunday, and that means it’s panic time for teams on the men’s NCAA Tournament bubble. But not all bubble teams are created equal. For instance, Wake Forest, which ranks 30th in ESPN’s BPI power rankings, ought to feel relatively good about its tourney chances, while Syracuse, which ranks 31st, should be in a state of full-blown terror. Why the difference? It all comes down to how each school did in a metric that best predicts the NCAA selection committee’s picking tendencies.

The selection committee has struggled for a while with how to pick the teams for the NCAA tournament. Should they be the best teams? Or simply the most deserving teams? The former may not have the best record, while the latter may not have the best talent. (In January, the NCAA even met with several analytics experts to help sort out this quandary.)

Stats, too, have to figure out which of these two questions they’re trying to answer. ESPN’s BPI and KenPom.com’s ratings are examples of predictive rating systems, meant to tell fans who the “best” teams are. Other rating systems such as ESPN’s new Strength of Record (SOR) are meant to rank “deserving” teams, grading a team’s resume according to how hard its record was to achieve. The two approaches can yield very different results, and my research shows that Strength of Record aligns more closely with what the committee looks for in a tournament team.

As the man behind updating ESPN’s College Basketball Power Index (BPI) before this season, I studied the Selection Committee’s historical behavior, to help build a system that assigns each team a probability of making the NCAA Tournament. I looked at many variables, including resume rankings such as Strength of Record and the NCAA’s official Ratings Percentage Index, predictive rankings such as BPI and KenPom, and simpler measures such as a team’s win-loss record.1

Most of these variables are highly correlated with each other, and in many cases they tell the same story about a school’s season. But Strength of Record has the highest correlation, and using it alone to select teams would help you agree with the committee 90 percent of the time. Plugging Strength of Record into a model (which includes other metrics, but weights them less2), we can assign tournament probabilities to teams considered “on the bubble” by ESPN’s Joe Lunardi. Because of differences in resume quality (as measured by SOR), some bubble teams are quite likely to be favored by the committee, while some should be worried if they fail to win their conference tournaments.

CURRENT RANKING AMONG D-I TEAMS
TEAM RPI BPI KENPOM STRENGTH OF RECORD CHANCE OF MAKING TOURNEY
Wake Forest 34 30 30 33 >99.9%
Xavier 33 36 43 37 99.9
Marquette 55 29 28 41 88.6
Illinois State 31 60 49 46 85.7
USC 39 58 61 43 76.4
Vanderbilt 44 49 40 56 65.6
Providence 52 55 53 40 63.0
Kansas State 60 41 32 45 61.9
Rhode Island 42 39 51 54 58.1
Indiana 81 32 46 57 19.1
Houston 50 35 41 59 17.2
Clemson 63 33 35 49 15.7
Syracuse 79 31 44 53 12.2
California 56 52 55 69 2.8
Illinois 58 63 68 58 1.5
Iowa 72 77 67 64 0.5
Chance of bubble teams making the NCAA Tournament, according to ESPN Stats & Information’s model

Bubble teams are drawn from Joe Lunardi’s bracketology classifications.

Source: ESPN Stats & Information Group, KenPom.com

So if your team is sweating things out on the bubble Sunday, keep an eye on its Strength of Record — not its RPI or its predictive ratings.

Footnotes

  1. Including its overall record and its record in conference and nonconference play.

  2. Specifically, here’s how the model works: We use BPI to simulate the rest of the season (including conference tournaments) 10,000 times, and in each simulation both automatic and at-large bids are selected. For the latter, we use a data-augmentation Bayesian Probit Regression model that includes SOR, RPI, BPI and an estimation of KenPom.com ratings to rank each team by its likelihood of grabbing one of the tourney’s 36 available at-large slots. A team’s chance to make the tournament, then, is a combination of their chance of winning their conference’s tournament and their chance of being selected as an at-large team if they don’t win the conference tournament.

Paul Sabin is an Analytics Specialist for ESPN’s Sports Analytics Team.

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